Interference preventer



T is July 3, 1923.

G. W. PICIKARD INTERFERENCE PREVENTER 3 Sheets-Sheet 1 Filed April 22', 1922 I J INVENTOR 'menleaflfhettzerzlkkard LATTORNEY 1 Filed April 22. 1922 3 Sheets-Sheet 2 INVENTOR Greenlea Wzhc'erRc/Eanl A TTORNEY M! GHSHMU July 3, 1923. I 1,460,439

I G. W. PICKARD INTERFERENCE PREVENTER Filed April 22, 1922 3 Sheets-Sheet 5 INVENTORQ Greenlm nt'fizrfibifard ATTORNEY Patented July 3, 1923.

ordnanc GREENLEAF WHITTIER PICKARD, OI NEWTON CENTER, MASSACHUSETTS, ASSIGNOR TO WIRELESS SPECIALTY APPARATUS COMPANY, OF BOSTON, MASSACHUSETTS, A

CORPORATION OF NEW YORK.

INTERFERENCE PREVENTER.

Application filed April 22, 1922. Serial No. 555,965.

To all whom it may concern:

Be it known that I, GREENLEAF WHITTIER PICKARD, a citizen of the United States of America, and a resident of Newton Center,

State of Massachusetts, have invented a certain new and useful Interference Preventer, the principles of which are set forth in the following specification and accompanying drawings, which disclose the form of the 'invention which I now consider to bethe best of the various forms in which the principles of the invention may be embodied.

This invention relates to interference preventer, involving method and apparatus for segregating desired from undesired airwaves, particularly in the case of radio communication where it is desired to obtain intelligible indications corresponding to inteleffected with reference to sound (air) waves which may be of such high frequency as to be inaudible to the human ear.

The object of the invention is to permit the receipt, aural or otherwise,of the desired intellig'ence, such as tele raph and telephone communication by radio or 1 wire (ether waves or. waves on wires), freed from the interfering, overlapping or obscuring sounds of interference.

The invention consists of the method, and of the apparatus for executing the method, all as described herein and defined in the claims as to novelty.

Fig. 1 is an illustration, partly diagrammatic, of a simplified form of apparatus by which the method can be executed;

Fig. 2 is a like illustration in greater detail; and" i Fig. 3 is a showingin detail of a form adapted for use with shorter radio wavelengths.

In Fig. 1 the diagrammatic portion at the left illustrates a radio receiving apparatus by which the electric waves are transformed into sound (air) waves (at telephone T usually in air. I

The central portion of Fig. '1 illustrates a reflection grating RG and the accompanying although the segregation of the invention is? amplifying and detecting the high frequency currents set up by the desired air-waves in the apparatus which receives them, and also apparatus for finally delivering the desired communications in amplified form to the person receiving them, as by delivering them 1 in the form of audible sound waves of ordinary telephonic frequencies of several hundred per second.

The invention involves a method of handling the sound waves which is analogous to an optical method. Optical methods them-.1 selves cannot be applied to the direct han 80 ,dling of radio transmitted electromagnetic waves themselves, to effectuate the object of\ the invention, because the structures required would be 'impracticably large. Such methods would involve the manifold magnification in size of the transmission or reflection grating spectrometer; and the wavelengths employed in radio communication are so long that such apparatus would occupy a considerable number of square miles' But in analogy to such optical methods, the invention hereof involves the transformation, without distortion, of the received electrical waves into sound waves in air which have approximately (for the same frequency) about one millionth the wave-length of the electrical waves themselves, owing to the fact that sound is propagated in air with approximately one millionth the velocity of electromagnetic waves in space. The invention therefore involves the transformation of the electric ether waves into much shorter air-waves, as a preliminary to the segregation of desired from undesired airwaves.

For example, a frequently used trans-At: lantic radio wave-length being ten thousand meters (a frequency of 30,000 per sec- 0nd), the air-waves set up by such frequency will have a length of approximately one centimeter.

In Fig. 1, the receiving antenna. A (which need not be tuned but is aperiodic) gathers in the electric waves corresponding not only to the communication desired to be received but also necessarily any undesired simultaneous communications by other frequencies and any atmospheric disturbances which are extant, both of which in practice frequently most seriously interfere with thereceipt or hearing of a desired communication in an intelliglible manner, and sometimes entirely prevent receipt and intelligible reception. Antenna A is connected to a suitable radio frequency amplifying device such as an audion or thermionic tube F, G, P, said parts being enclosed in a vacuum tube, as usual, and comprising the heated filament F, the controlling grid G and the plate P, suitable batteries being provided as indicated or desired. This tube preferably (for best operation of the invention) is designed, constructed and arranged for amplification only of radio frequency currents, as shown. Antenna A is also connected to ground as usual and as shown. The thermionic tube is coupled to antenna A by the coupling resistance R, which is preferably of such magnitude as to make the antenna system aperiodic. An aperiodic antenna system cannot be set into sustained oscillation by a transient pulse, and therefore passes on to the amplifier, undistorted, the desired signal waves, interfering signal waves, and those transient pulses which are known as static or atmospheric disturb ances. If the antenna system were oscillatory, these static pulses would be converted into sustained oscillations, whereas an object hereof is to prevent the static from assuming a sustained form.

But the desired communications at say 30,000 per second or less set up currents of the same frequency in antenna A across resistance R and across the grid G and filament F of the tube, which amplifies at the 30,000 frequency but does not change it, and air waves of the 30,000 frequency and without distortion will emanate from the diaphragm of ordinary electromagnetic telephone T which diaphragm is vibrating (audibly if sufliciently intense) at that rate. These extremely high pitch sounds exactly corre spond in frequency withl the desired communication and other received electric waves, a ten thousand meter electric wave having a frequency of 30,000 cycles. Thus the said air waves will, of course, have a frequency of 30,000 per second, their length being approximately one centimeter. In addition to these sound waves resulting from the desired communication, telephone T may produce sounds from other resulting communications not desired to be received and also from other disturbances such as static.

In the path of these various high frequency short air waves is placed a reflection grating RG, inclined as shown; so that the waves are directed against the grating and are reflected therefrom at an angle to their direction of propagation. Grating RG has a plurality of reflection members which are separated from one another by distances phone T toward grating RG (as indicated by the wavy lines in Fig. 1), and more 01 less diffused depending upon other factors. The reflection of the desired air-Waves from grating RG adapted to them by construction takes place principally at one definite angle to the propagation from telephone T, which angle corresponds to the position of the wave-length in the first order spectrum as it would be called in optics.

The operation of grating RG depends upon interference; that is, when the airwaves from telephone T strike the reflection elements of the grating, each element becomes, in effect, a point or line source of air-waves. As these elements are distributed periodically in tune with the desired air wave frequency, and as they are struck at different times by the advancing wave front of the desired air-waves from telephone T there will be (for any particular frequency of such desired air-waves) a definite direction or angle of reflection from grating RG at which the reflected air-waves from the several reflection members of the grating will be added together to reinforce one another; practically the entire portion of the energy of the desired air-waves being concentrated in a definite direction as indicated by the wavy lines leading to telephone T, which is located in the path of these desired air-waves for the purpose of receiving them, so that its diaphragm also will vibrate at the frequency of 30,000 per second.

A different train of air-waves from telephone T of different wave length, and resulting from communications not desired to be received, will be reflected from grating RG (which is constructed to be adapted only to the wave-length of the desired air waves) at a different angle from that of the desired air-waves, and will not enter the receiving telephone T"; also such train of air-waves from undesiredcommunications which are the result of static on antenna A (and may not be in the form of more or less prolonged wave trains but of such short or damped form as indicated at T), will strike reflection grating RG but will be spread out and diffused into a continuous air-wave spectrum over the arc C-S, so that only an infinitesimal portionof the energy of such air-waves will enter the telephone T These reflected air-waves due to static, on striking grating RG, will be resolved into a series of periodlc pulses which will be reflected at all angles to 1 form the sort of air-wave spectrum C-S.

Thus there is effected the segregation of a the desired air-waves from either and both of the undesired com-muncations and from static disturbances respectively. 1

The desired communication may be. ob-

- phone T are caused to produce low frequency audible sounds via the diaphragm of telephone T The circuits of the radio fre quency amplifier may be tuned. Also beat reception, regenerative reception, or. other method may be employed in apparatus AM.

Such segregation is so effective by this method that any degree, of amplification may be employed, before and after reflection from grating RG, either'or both, with the result that the desired communication is amplified without distortion while the undesired communications are eliminated. Thus,

- for increasing the effect of the segregating reflection from grating RG, and in cases when the radio received signals are very weak, the plate circuit of the audion FGP may be cut at X, X and there may be inserted any desired number of stages of radio frequency amplification, as by the use of the known succession of audions and transform ing coils. The circuits of these amplification stagesmay be tuned or untuned. I

In Fig 2, the electrical apparatus is shown in greater detail. As in Fig. 1 antenna A may receive 10,000 meter radio waves havin a frequency of 30,000, setting up current 0 that frequency in the antenna, and developing a corresponding potential difference across resistance R, and across grid G and the plate of the first of a train of radio frequency audio-n amplifier tubes. The tubes, shown in a train of three, may be coupled successively by the well-known resistance coupling shown. The 30,000 cycle current is thus thrice amplified without distortion, so that the diaphragm of telephone T is vibrated vigorously at that rate to produce air waves of the same frequency but one centimeter in length. The air-wave action is then as described in Fig. 1 (the air-waves of undesired communication or static being eliminated); and the diaphragm of telephone T will be vibrated by the 30,000 desired frequency which will set up currents of that frequency in the circuit of the telephone winding which may lead to the apparatus shown or other desired electrical apparatus. Here (Fig. 2) the circuit of telephone T is connected to the train AT of two radio frequency audion amplifiers and a third tube DT constituting the detector and connected to the operators phones T. An external heterodyne source H (for beat reception) with audion oscillator is feebl coupled by condenser C with grid Gr of t e first tube of amplifier train AT. This source may be adjusted to gen erate local oscillators of say 31,000 fre quency which is delivered to grid G where it mixes with the 30,000 cycle current from telephone T The tubes of train AT thereupon amplify the mixed currents without distortion. 'Then the mixed amplified currents pass to audion detector DT (provided with grid condenser GC and grid leak GL), whereby the beat frequency of 1,000 (31,000 minus 30,000) is passed on to telephone T i As in Fig. 1, although the radio waves are 10,000 meters from crest to crest, the air-waves of the same frequency (30,000) from telephone T are about one centimeter from crest to crest, so that the c0mmunications in the form, of these airwaves are in short-wave form which can. be handled by quasi-optical methods which do not require use of reflection gratings RG of excessive size.

The invention lends itself to numerous variations, of which one or two examples are given below for the purpose of further describing it.

For example, in case of extremely short wave radio reception (much shorter than that now emplo ed transoceanically), where the sound wyfig resulting from the conver sion up to and from telephone T might be too short to be easily handled (as, for ex-' short high frequency waves into waves of:

more readily workable frequency, such, for example, as 10,000 to 50,000 vibrations per second, thereby corresponding generally with the order of magnitude of transoceanic working above referred to. For example, a 300 meter wave may have added to it from a local source an oscillation at about 310 meters, giving a beat rate of about 30,000 cycles, which is converted into air-waves to be segregated as above. This is illustrated in Fig. 3. Here the radio waves of the desired communication, 300 meters long and having a frequency of a million per second, produce oscillating currents of like frequency in antenna A. An external oscillating current adjusted to give say 1,030,000 cycles (wave-length of 310 meters) is coupled by condenser C to antenna A where both high frequency currents are mixed and passed through a train of three audion amplifiers of radio frequency like the train of Fig. 2 where the mixed currents (together with the radio frequency currents of undesired communications) are amplified. Then all the amplified currents are passed to audion detector DT (provided with grid condenser GD and grid leak GL), where the detector brings out the beat fre quency of 30,000 (1,030,000 minus 1,000,000) which is passed on to telephone T which produces air-waves of that frequency as in Figs. 1 and 2. The subsequent apparatus and operation then is the same as in Figs. 1 and 2.

Thus, for the case of short radio waves, the action is the same as for long waves, save that the eflective frequency in the case of short waves is first made to be lower so as to be of the same order as the natural frequency of the long waves.

In general, for further increasing the efficiency, telephone T of Figs. 1, 2 and 3 may be placed at the focus of a parabolic mirror, or of a suitable sound lens, such as a thin india-rubber lens filled with carbon dioxid for making the sound beam parallel and thereby concentrating its energy on the face of grating RG.

Also, if desired, the method hereof may be made more efficient and further refined by providing a second gratin like RG to receive the reflections from Gr and in turn reflect them to an air-wave receiver such as telephone T thereby, if necessary, obtaining a more nearly complete separation of the desired from the disturbing air-waves.

This invention is very useful because it provides for the necessary segregation under circumstances when no other means is effective. For example, when interfering signals or static come from the same direction as the desired signal, then directional methods of segregation are of no avail. Also it has been demonstrated that the employment of resonant circuits is in itself insufficient to effect segregation. Also, my invention accomplishes a result in segregation which is not possible with any combination of artificial lines or filters of which I have knowledge.

I claim 1. Means for segregating desired intelligence communicated by electric waves from interfering disturbances, which comprises means for converting such waves into electric currents; means for amplifying such currents; an electromagnetic telephone receiver arranged to be supplied with such amplified currents; a reflection grating located in the path of air-waves from said telephone receiver; an electromagnetic telephone receiver located to have its diaphragm in the path of air-waves reflected from said grating; and means for converting the currents set up by the telephone receiver into intelligible indications of the desired communication.

2. The method for segregating desired intelligence communicated by electric waves from interfering disturbances, which consists in converting the received waves into air-waves of high frequency, segregating the desired from the undesired air waves, converting the desired air waves into high frequency electric currents; and converting Said currents into intelligible indications of the desired communication.

3. Means for segregating desired intelligence communicated by electric waves from interfering disturbances, which comprises means for converting the received waves into air waves of high frequency; means for segregating the desired from the undesired air waves; a telephone receiver located to have its diaphragm in the path of the segregated air waves; a detector of the high frequency currents produced by the telephone; and a telephone supplied by the detected currents.

4. The method of segregating desired intelligence communicated by electric waves from interfering disturbances, which consists in transforming such waves into air waves of high frequency, causing the latter to be reflected from a plurality of reflection points into a definite direction of reflection, nd transforming such reflected waves into electric currents.

5. The method of segregating desired intelligence communicated by electric waves from interfering disturbances, which consists in transforming such waves into sound waves of high frequency, causing the latter to be reflected into a definite direction from a plurality of reflection points separated from one another by distances corresponding to the lengths of such sound waves; and transforming such reflected waves into electric currents.

6. The method of segregating desired intelligence communicated by electric waves from interfering disturbances, which consists in transforming such waves into air waves of high frequency, causing the latter to be reflected from a plurality of points, and such reflections to be combined in a definite direction at an angle to their original direction of propagation; transforming such reflected waves into the energy of motion, and causing such motion to produce electric currents.

7. The method of segregating desired intelligence communicated by electric waves from interfering disturbances, which consists in transforming such waves into sound Waves of high frequency; causing the latter to be reflected from a plurality of points and such reflections to be combined in a definite direction at an angle to their original direction of propagation; and transforming such' reflected waves into electric currents at a point in the line of the direction of reflection.

8. The method of segregating desired electrically communicated intelligence from interfering electrical disturbances, which consists in segregating a train of air waves of a given frequency and due to the desired electrical communication from other air waves of a different frequency and due to the electrical disturbances, by reflecting such train from a plurality of points separated from one another by distances corresponding to the length of the waves in such train.

9. The method of segregating desired electrically communicated intelligence from interfering electrical disturbances, which consists in segregating a train of air waves of a given frequency and due to the'desi'red electrical communication from another sound of a different frequenc and due to the electrical disturbances, by irecting such train against a plurality of reflecting points separated from one another by distances corresponding to the length of the waves in such train, and placing a telephone receiver in the path of the reflection from such points.

10. Means for segregating desired electrically communicated intelligence from interfering electrical disturbances, by segregating a train of high frequency air waves due to the desired electrical communication, which comprises a reflection grating located at an inclination to the direction of propagation of such train and in the path of the same and having its elements separated from one another by distances corresponding to the length of the waves in said train.

11. Means for segregating desired intelligence communicated by electric waves from interfering disturbances, which comprises wave-receiving apparatus constructed and arranged to transform such waves into sound waves of high frequency, and including an air-wave source; and a reflection grating located in the path of and at an inclination to the direction of propagation of such waves and constructed to have its elements separated from one another by distances corresponding to the length of such sound waves.

12. Means for segregating desired intelligence communicated by electric waves from interfering disturbances, which comprises electric-wave-receiving apparatus constructed and arranged to transform such waves into air-Waves of high frequency, and including an air-wave source; a reflection grating constructed to accord with the frequency of such air waves; an electromag netic telephone receiver having its diaphragm located in the path of reflection of such waves from said grating; and means for converting the currents set up by the telephone receiver into intelligible indications.

13. Means for segregating desired intelligence communicated by electric waves from the transient pulses from static inter- .ferenoe, which comprises electric-wave recumin Wl-llTTlER PICKARD. 

